Image-guided surgery is often conducted based on pre-operatively taken image data, such as Magnetic Resonance Imaging (MRI) or Computerized Tomography (CT) data. These pre-operatively taken image data can be very accurate if no significant changes occur during surgery. However, during surgery many different factors may affect, for example, tissue movement, and hence cause changes that are not reflected in the images acquired prior to the surgical procedure. In soft tissue areas, these movements are particularly common (in neurosurgery such changes are also referred to as the brain shift problem).
In order to avoid such problems, it has been suggested to work with continuously updated image data during the surgical procedure. To this end, intra-operative imaging approaches are used. These approaches include, for example, real-time ultrasound imaging.
Intra-operatively taken image data give the surgeon live feedback upon placing a surgical device (e.g., a biopsy needle) in a target area of a patient as soon as the surgical device is also in the field of view of the imaging device. A major limitation is that it is difficult to obtain an optimal view of, for example, a tip portion of the surgical device and the target area at all times in the real-time patient image. When, for example, two-dimensional images are used, only the proximal part of the surgical device intersecting the image plane gets visualized.
Since the surgical procedure is often done free hand, where the ultrasound probe and the surgical device can be freely moved and oriented simultaneously, visualization becomes even more difficult. Still, an optimal view is of crucial importance to know where the surgical device is located relative to important anatomical structures. Often an in-plane approach is used to visualize the surgical device in the intra-operative image, wherein the surgical device is mechanically guided within the image plane. However, this guidance limits the possible positional configuration of the imaging device and surgical device.
To guide the surgeon optimally, it would be valuable to know how to adjust the surgical device in order to direct the surgical device to the anatomical region of interest, even before the surgical device gets reproduced in the image. To achieve this, a localization and visualization of the tool relative to the intra-operative image would be desirable. Providing this additional information helps the surgeon for example to hit the target by a direct approach, and prevents the damaging of additional tissue. It also gives additional information to achieve an even more accurate placement of the surgical device.